260
Turtles,
Tortoises
and
Terrapins
Cycles and Seasons
Camila Ferrara and Richard Vogt have recent-
ly discovered that Arrau (Podocnemis expansa)
hatchlings call as they emerge from their nests.
They believe that they use these calls to synchro-
nize hatching, digging their way out of the sand
and emerging from the nests, and, amazingly, to
exchange low-frequency calls with adults wait-
ing for them in the river. The hatchlings join the
migrating adults, who lead them to feeding grounds
in the flooded forest. Nothing remotely like this is
known from any other turtle, including other spe-
Animals that lack parental care must compen-
sate for its absence. Their eggs must be well suited to
survive their incubation period unaided. They may
construct carefully concealed and optimally situ-
ated nests, hidden from predators and parasites and
placed to provide the best available environment for
embryological development (though a good number
of rainforest turtles simply deposit their eggs on the
ground). To increase the likelihood that at least some
young may survive and reproduce, they may lay a
large number of eggs over their reproductive life-
times. Turtles, to greater or lesser degrees, have done
all of these; indeed, sea turtles (see page 306, Chapter
8) lay the largest clutches of eggs of any reptile.
The reproductive life of land and freshwater turtles
is governed by the seasons, whether they are the four
seasons of the temperate zone or the wet and dry
seasons of the tropics. Males and females go through
annual cycles of sperm and egg production that do
not necessarily peak at the same time. In temperate-
zone turtles, males produce sperm over the summer
that they will need for mating the following spring.
Male Spotted Turtles (Clemmys guttata) in south-
eastern Pennsylvania produce most of their sperm in
June and July, concluding in August; their peak mat-
ing season is from March through May. This pattern
may ensure that the male has viable sperm available
when the female ovulates. Most female turtles ovu-
late in spring, so sperm formation ought, ideally,
to take place during the winter; however, the cold
prevents this from happening, so males must have
their sperm supply ready by the end of the previous
fall. They store the sperm in their genital tract until
they need it. Painted Turtles (Chrysemys picta) pro-
duce sperm over the summer, but males carry viable
sperm in the epididymis throughout the year.
Female turtles, too, may store sperm, in tubules
in their oviducts. Desert and Gopher (Gopherus poly-
phemus) tortoises do most of their mating in the fall
when male sperm production is at its peak, but the
females store sperm, and delay laying their eggs, until
they emerge from their burrows the following spring.
Sperm storage lets the female time fertilization and
egg-laying so that her hatchlings develop and emerge
under the best possible conditions. It also allows
her to lay multiple clutches of eggs from a single
mating—a useful insurance strategy for many tur-
tles. Female Chinese Softshells (Pelodiscus sinensis)
can store viable sperm in their oviducts for almost
a year, and Painted Turtles for three years. Eastern
Box Turtles (Terrapene carolina) and Diamondback
Terrapins (Malaclemys terrapin) have produced fer-
tile eggs four years after their last mating. Captive
female Indian Softshell Turtles (Aspideretes gangenti-
cus) studied by Nikhil Whitaker laid fully viable eggs
fertilized by sperm they had stored in their reproduc-
tive tracts for 15 years.
Sperm storage allows a female to collect sperm
from several males, and lay clutches of eggs sired by
more than one father. Though multiple paternity
increases a male’s chances of mating, its benefits, and
possible costs, to females are not fully understood.
Turtle promiscuity has nonetheless been found in
podocnemidids, snapping turtles, sea turtles includ-
ing the Leatherback (Dermochelys coriacea), emydid
pond turtles and tortoises, including Gopher and
Spur-thighed Tortoises (Testudo graeca). In one pop-
ulation of Blanding’s Turtles (Emydoidea blandingii)